In conventional practice, exposure systems that use microlens arrays have been used as laser annealing systems for reforming an amorphous silicon film into a polysilicon film by irradiating the amorphous silicon film with laser light and melting and solidifying the amorphous silicon film by the heat of the laser light. Such exposure systems have also been used as exposure systems for photolithography wherein a mask image is projected and exposed on a resist film, and a resist pattern is formed by a subsequent developing process (Patent Document 1).
FIG. 6 is a cross-sectional view showing a projection-exposure type exposure system using a conventional microlens array. A resist film 2 is formed on a substrate 1, and the substrate 1 is conveyed below a microlens exposure system. A conventional microlens exposure system is provided with a microlens array 3 formed by two-dimensionally arranging numerous microlenses 3a, and a mask 4 is arranged above the microlens array 3. The microlens array 3 is formed from a transparent quartz substrate, and the microlenses 3a are machined into the bottom surface of the microlens array 3. The mask 4 is configured by bonding a Cr film 5 to the bottom surface of the transparent substrate, and holes 5a through which laser light passes are formed in the Cr film 5 in positions matching the microlenses 3a. Portions of the mask 4 other than the holes 5a are covered by the Cr film 5, constituting light-blocking portions that prevent laser light from passing through. The mask 4 and the microlens array 3 are fixed in place by a fixing member 6 so as to have a predetermined space in between. The microlens array 3 and the mask 4 can be moved along the optical axis by a suitable drive system, and their distances to the substrate 1 can be adjusted.
In a conventional microlens exposure system configured in this manner, when the laser light for exposure is irradiated onto the mask 4, the laser light that has passed through the holes 5a in the mask 4 is irradiated onto the microlenses 3a of the microlens array 3 and made by the microlenses 3a to converge on the resist film 2 on the substrate 1. A pattern to be projected is formed in the holes 5a, and when the laser light is transmitted through the holes 5a and radiated onto the resist film 2, the pattern is projected onto the resist film 2.
In order for the laser light passing through the microlenses 3a to converge on the resist film 2 on the surface of the substrate 1, a gap G between the substrate 1 and the microlens array 3 must be made to coincide with the focal point position of the microlenses 3a, and this gap G must be managed. In conventional projection-exposure type exposure systems, the gap G has been managed by measuring the distance between the surface of the mask 4 and the surface of the substrate 1 and setting this distance to a predetermined value. However, because quartz substrates on which microlenses are formed have different thicknesses depending on manufacturing conditions, the reality in conventional practice has been that the gap G between the substrate 1 and the microlenses 3a has not been managed. Therefore, in a conventional exposure system, after the distance between the surface of the mask 4 and the surface of the substrate 1 has been set to the predetermined value, exposure and development are performed, and whether or not the resist film 2 on the substrate 1 is in the aligned focal point position of the microlenses 3a is inspected by observing the resulting pattern through a microscope. When the substrate 1 is not in the aligned focal point position of the microlenses 3a, a focus adjustment is performed by trial and error in which the positions of the mask 4 and the microlens array 3 are adjusted, and exposure, development, and microscope observation are performed again to confirm the aligned focal point position. Therefore, much labor has been required in managing the gap G in conventional exposure systems.
In view of this, Patent Document 1 proposes an image exposure system, the object of which is to align with the focal point position with precision. In this image exposure system, a microlens for focal point position detection is provided separate from the microlenses for image exposure, laser light from a light source is transmitted through the microlens for focal point position detection as well, and the laser light is imaged on an imaging position on a resist film. This image is then photographed by a camera, and the position of the microlens array is adjusted along the optical axis so that the focus of the photographed image matches.